Use of enums

Hi,

I've made some changes. I removed the Constants class and added enums.
Enums are probably a bit cleaner to use and maybe also a little more save.
Just have a look at it, I didn't get a part in the controller though.
Also didn't update the comments, but not sure if that's really needed.
Also the enum files could probably use a better place, because this seems a little messy.